An electric wave (beam) emitted from a base-station antenna device, which is one of antenna devices, is often tilted (with a tilt angle). For example, an electric wave emitted from a base-station antenna device of a mobile phone is generally tilted with a downward tilt angle. This is for avoiding an electric wave emitted from the base-station antenna device from reaching outside an area (cell) allocated to the base-station antenna device. Patent Document 1 (U.S. Pat. No. 5,940,030) describes an example of a phase-shift circuit for providing a tilt angle to an electric wave emitted from an antenna device including a base-station antenna device.
The phase-shift circuit described in Patent Document 1 includes: a signal line; ground conductors facing each other across this signal line; and a dielectric plate (impedance-matching member) inserted into a gap between the signal line and each ground conductor. The dielectric plate is inserted into the gap from a direction perpendicular to an extending direction of the signal line so as to intersect the signal line.
Patent Document 1 describes that a phase of a signal outputted from the signal line is changed by increase/decrease in an amount of the intersection between the dielectric plate and the signal line, that is, in the overlapping area between the dielectric plate and the signal line, which results in a change in a tilt angle of an electric wave emitted from the antenna device. Specifically, the electric plate has a substantially triangular shape whose width gradually increases from a front side to a rear side in an inserting direction. Therefore, when the dielectric plate is moved forward in the inserting direction (when the amount of insertion is increased), the overlapping area between the dielectric plate and the signal line is increased, so that the phase of the signal outputted from the signal line is delayed.